The present invention relates to a method for inducing cardioplegic arrest in a heart and to catheters for use in that method.
The use of extracorporeal cardiopulmonary by-pass for cardiac support has become well established. This use has, however, involved median sternotomy or less commonly thoracotomy with all of the trauma that necessarily accompanies such a major surgical procedure.
The present invention contemplates, at least in its preferred embodiments, the possibility of effective ascending aortic occlusion, cardioplegia, venting, right heart deflation and topical cooling in association with extracorporeal cardiopulmonary by-pass all without necessitating a median sternotomy or other thoracic incision.
In a first aspect the present invention consists in a method for inducing cardioplegic arrest of a heart in situ in a patient""s body, comprising the steps of:
(a) maintaining systemic circulation with peripheral cardiopulmonary by-pass;
(b) occluding the ascending aorta through a percutaneously placed arterial balloon catheter;
(c) introducing a cardioplegic agent into the coronary circulation; and
(d) venting the left side of the heart.
The method according to the present invention may be carried out on humans or other mammalian animals. The method is of particular applicability in humans as it allows an alternative approach to open heart surgery and the development of closed cardioscopic surgery. The method according to the invention enables a percutaneous by-pass system to be associated with cardioplegia, venting and cooling of the heart which subverts the need for median sternotomy. This may, in turn, reduce the complications of the surgery.
The maintenance of the systemic circulation involves establishing a cardiopulmonary by-pass. The blood may be drawn into the by-pass merely by positioning a percutaneous catheter into the right atrium and/or into one or both of the vena cavae through which venous blood may be drawn from the heart into an extracorporeal pump oxygenator. In more preferred embodiments of the invention a single catheter with two inflatable cuffs, or two separate catheters, each with an inflatable cuff are introduced into the vena cavae to occlude them adjacent to their right atrial inlets. This allows isolation of the right atrium and allows blood to be drawn from the vena cavae into the by-pass system. There is also preferably provision for percutaneous communication via one catheter with the right atrium to allow infusion of saline into the right atrium. This infusion has the advantage that it allows the heart to be cooled and improves visual acuity within the right heart allowing direct cardioscopic examination and/or intervention.
The catheter used to decompress the right atrium and to draw blood into the by-pass is preferably introduced through the femoral vein by percutaneous puncture or direct cut down. If other than simple venous drainage is required catheters with inflatable cuffs, as described above, are placed preferably such that in inflatable cuff of the cannula is positioned within each of the inferior (suprahepatic) and superior vena cavae. There is preferably a lumen in the cannula acting as a common blood outlet from the vena cavae leading to the pump oxygenator. A separate lumen is preferably used to infuse saline between the two inflated cuffs into the right atrium. If, alternatively, separate catheters are used to occlude each of the inferior and superior vena cavae than the cannula for the inferior vena cavae is preferably introduced percutaneously from the femoral vein and that for the superior vena cavae is introduced percutaneously through the jugular or subclavian vein.
The ascending aorta is preferably occluded by a balloon catheter introduced percutaneously through the femoral artery. This catheter must carry adjacent its tip an inflatable cuff or balloon of sufficient size that upon being inflated it is able to completely occlude the ascending aorta. The length of the balloon should preferably not be so long as to impede the flow of blood or other solution to the coronary arteries or to the brachiocephalic, left carotid or left subclavian arteries. A balloon length of about 40 mm and diameter of about 35 mm is suitable in humans. The balloon is of a cylindrical shape to fully and evenly accommodate the lumen of the ascending aorta. This maximizes the surface area contact with the aorta, and allows for even distribution of occlusive pressure.
The balloon of the catheter is preferably inflated with a saline solution to avoid the possibility of introducing into the patient an air embolism in the event that the balloon ruptured. The balloon should be inflated to a pressure sufficient to prevent regurgitation of blood into the aortic root and to prevent migration of the balloon into the root whilst not being so high as to cause damage or dilation to the aortic wall. An intermediate pressure of the order of 350 mmHg has been proven effective in trials.
The aortic catheter is preferably introduced under fluoroscopic guidance over a suitable guidewire. Transoesophageal echocardiography can alternatively be used for positioning as has been described with reference to the venous catheter. The catheter may serve a number of separate functions and the number of lumina in the catheter will depend upon how many of those functions the catheter is to serve. The catheter can be used to introduce the cardioplegic agent, normally in solution, into the aortic root via one lumen. The luminal diameter will preferably be such that a flow of the order of 250-500 ml/min of cardioplegic solution can be introduced into the aortic root under positive pressure to perfuse adequately the heart by way of the coronary arteries. The same lumen can, by applying negative pressure to the lumen from an outside source, effectively vent the left heart of blood or other solutions. It may also be desirable to introduce medical instruments and/or a cardioscope into the heart through another lumen in the catheter. The lumen should be of a diameter suitable to pass a fibre-optic light camera of no greater than 3 mm diameter. It is however, preferable that the diameter and cross-sectional design of the internal lumina is such that the external diameter of the catheter in its entirety is small enough to allow its introduction into the adult femoral artery by either percutaneous puncture or direct cut-down
The oxygenated blood returning to the body from the by-pass system may be conveyed into the aorta from another lumen in the cannula carrying the balloon. In this case the returning blood is preferably discarded from the catheter in the external iliac artery. In another embodiment of the invention, and in order to reduce the diameter of the catheter carrying the balloon, a separate arterial catheter of known type may be used to return blood to the patient from the by-pass system. In this case a short catheter is positioned in the other femoral artery to provide systemic arterial blood from the by-pass system. The control end of the catheter, i.e. that end that remains outside of the body, should have separate ports of attachment for the lumina. The catheter length should be approximately 900 mm for use in humans.
The cardioplegic agent may be any of the known materials previously known to be useful, or in the future found to be useful, as cardioplegic agents. The agent is preferably infused as a solution into the aortic root through one of the lumina of the aortic catheter.
In another aspect the present invention consists in a catheter for use in occluding the ascending aorta comprising an elongate tube having one or more continuous lumina along its length, an inflatable cuff is disposed about the tube adjacent one end thereof, the cuff being of such a size that upon being inflated it is able to occlude the ascending aorta of a patient.
The catheter and method according to the present invention can be used to induce cardioplegic arrest and may be used in a number of surgical procedures. These include the following:
1. Coronary artery revascularization such as:
(a) angioscopic laser introduction or angioscopic balloon angioplasty catheter into the coronary arteries via one lumen of the aortic catheter; or
(b) thoraco dissection of one or both of the mammary arteries with revascularization achieved by distal anastomoses of the internal mammary arteries to coronary arteries via a small left anterior thoracotomy.
2. Secundum-type atrial septal defect repair such as by:
(a) xe2x80x9cClosedxe2x80x9d cardioscopic closure, or
(b) Closure as an xe2x80x9copenxe2x80x9d procedure via a mini-right thoracotomy.
3. Sinus venosus defect repairs similar to 2 above.
4. Infundibular stenosis relief by cardioscopic techniques.
5. Pulmonary valvular stenosis relief by cardioscopic techniques.
6. Mitral valve surgery via a small right thoracotomy.
7. Aortic stenosis relief by the introduction of instrumentation via a lumen in the aortic catheter into the aortic root.
8. Left ventricular aneurysm repair via a small left anterior thoracotomy.